Dean links us to the original income tax form, which he found here.
It's not so easy to read, but it appears that no one with less than about $3000 of income had to pay any taxes. That was close to 3 times the average income of the day - see this for some examples of 1913 prices. It doesn't take a tax lawyer to figure out that the taxes start a lot lower income today.
Likewise note the highest percentage of tax - 6%. That's well below the lowest rate we have today, and a fraction of the highest.
Remember this the next time some SOB says he'll only raise the taxes on "the rich". That's how this abomination got into the door in the first place, and how it has expanded to provide the funds to permit the govt to become the monstrosity it has become today.